Currently, the automatic transmission is filled during vehicle assembly by use of automatic equipment. A specific volume of fluid, which is intended to overfill the transmission, is introduced through the filler tube. The transmission is then cycled to ensure all passages are filled. Fluid is subsequently withdrawn through the filler tube until the fluid level drops lower than the tube end, exposing it to air, thus causing a pressure change which is detected by the processing equipment. This signals an end to the fluid withdrawal portion of the fill cycle, setting the fluid level within the transmission.
As shipped from the assembly plant, the transmission fluid level can and does vary due to many identified sources. The location of the filler tube end relative to the machined features of the transmission case is a major contributor, being affected by filler tube length, tube mounting location, and casting variances as well as case machining tolerances. Furthermore, the sensitivity of shut-off for the filling equipment, coupled with the orientation and configuration of the tube end, add more variance to the fluid level. Lastly, the differences in volumes of internal components between individual transmissions add another significant fluid level variance particularly because the transmission is filled when relatively cold, but its operational fluid level limits are defined as being in a "hot" condition and the fluid expands around these internal components when heated. This last variance, however, is not addressed by the present invention.
Presently, the fluid level indicating hardware consists of a ullage rod or dipstick which is snaked through the filler tube and protrudes into the transmission bottom pan where the rod tip is expected to be immersed in the transmission fluid. In order to provide a frame of reference, this rod is stopped, or grounded, in one of two places. One is at the remote end of the filler tube, where the location and length variances of the filler tube and the like, add to the variances of the dipstick length and markings, to total the errors of fluid level indication. To eliminate some of these variances, another method attaches a stop for the rod tip to components located on the transmission underside. This latter method has reduced the indicating errors, providing the dipstick does indeed, make contact with the stop. Packaging constraints have prevented addition of a dipstick-guided feature. This lack of a guiding feature often eliminates the reduction of indicating error provided by the stop, because the dipstick tip may not hit or stay on the stop.
In order to provide an improved product and customer satisfaction, it is desired that these cumulative variances and errors, as a whole, be reduced.
The existing state of the art suggests that improved indicating hardware can provide more consistent filling of automatic transmissions with fluid, initially during automobile assembly, and subsequently, whenever the transmission is serviced or checked.